Re: [Haskell-cafe] Functional version of this OO snippet

5 Dec 2008

      On 5 Dec 2008, at 13:40, Andrew Wagner wrote:
...
Hi all,
public interface IEngine {
 void foo();
 void bar(string bah);
 ...
}
public class Program {
public void Run(IEngine engine){
 while(true){
   string command = GetLine();
   if (command.startsWith("foo")){
     engine.foo();
   } else if (command.startsWith("bar")){
     engine.bar(command);
   ...
   else break;
}
In other words, I want to provide the same UI across multiple  
implementations of the engine that actually processes the commands.
class IEngine a where
   foo :: a -> String
   bar :: a -> String -> String

run :: IEngine a => a -> IO ()
run x = interact (unlines . processCommand x . lines)

processCommand e c
   | "foo" `isPrefixOf` c = foo e
   | "bar" `isPrefixOf` c = bar e c

That should about do it.

Bob

Re: [Haskell-cafe] Functional version of this OO snippet

Thomas Davie